Looks like there is no hard-coded limit on the size of the JSON response that Rest Client can consume in Spring Boot. However, practical limitations arise due to several factors, including:

Heap Memory Limit

The JVM's heap memory size determines how much data your application can hold in memory at any given time. Large JSON responses can lead to OutOfMemoryError if they exceed the allocated heap size.

Increase the heap size if needed by setting JVM options:

Timeouts

Large responses might take more time to download and process, which can result in timeouts.

Solution:We can tune RestTemplate's timeout settings via RequestFactory:

import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

public RestTemplate restTemplate() {
    HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory();
    factory.setConnectTimeout(5000); // 5 seconds
    factory.setReadTimeout(30000);  // 30 seconds
    return new RestTemplate(factory);
}

Serialization/Deserialization Overhead

Jackson or other JSON parsers will load the entire JSON into memory for parsing. This can be a problem for very large JSON payloads.

We can consider streaming large JSON responses using JsonParser from Jackson:

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParser;

public void parseLargeJson(InputStream inputStream) throws IOException {
    JsonFactory factory = new JsonFactory();
    try (JsonParser parser = factory.createParser(inputStream)) {
        while (!parser.isClosed()) {
            JsonToken token = parser.nextToken();
            // Process token as needed
        }
    }
}

Use WebClient (preferred for reactive programming and streaming support):

import org.springframework.web.reactive.function.client.WebClient;

WebClient client = WebClient.create();
client.get()
      .uri("http://example.com/large-json")
      .retrieve()
      .bodyToFlux(String.class) // Stream the response
      .subscribe(data -> System.out.println("Received chunk: " + data));

• We can also implement Pagination: Request data in smaller chunks if the API supports it (e.g., limit and offset query parameters).
• We can also utilize Chunked Processing: Process the response in smaller chunks to reduce memory overhead.

Thanks for reading the content and I hope it is useful.